On the same day police announced the arrest of a car-service driver in the rape of a woman in front of her Northwest D.C. home, prosecutors said they are declining to bring charges and the man taken into custody would be set free.

D.C. police officials said Thursday morning that they had arrested Anouar Habib Trabelsi, 35, of Alexandria, a driver with the Uber car service, after taking samples of his DNA in December as part of their investigation of the case. But as police officials spoke at a late afternoon news conference about the arrest, the U.S. attorney’s office said that, after reviewing the case, prosecutors are “not moving forward with charges at this time.”

Neither police nor prosecutors would say more about why the charges were being dropped.

According to a search warrant filed by police in D.C. Superior Court enabling investigators to obtain a sample of Mr. Trabelsi’s DNA, a woman was raped outside her Cleveland Park home after paying an Uber driver for a ride home from a U Street bar. The woman had three vodka drinks and had smoked marijuana earlier in the night and was told by bar employees “to leave because she was inebriated,” the court documents state. She summoned a Uber driver to take her home and paid the driver before getting out of the car. Once she got out, the woman said the driver grabbed her, causing her to fall and strike her head on the concrete driveway. The driver then pulled down her pants and raped her, the documents state.

Once at a hospital where she reported the sexual assault, the woman viewed Mr. Trabelsi’s photo, which was on her Uber receipt, and said she was 75 percent to 80 percent sure he was the person who had assaulted her, but she noted it was difficult to tell because the photo was small, court documents state. Investigators obtained potential DNA evidence from the woman, but court documents do not say whether Mr. Trabelsi’s DNA sample matched the sample that was taken.

Uber has gained notoriety in the District as an alternative to taxicabs and advertises itself as “your on-demand private driver,” allowing customers to request a ride from sedan companies that partner with the firm by using a smartphones app or the Web. A Uber spokeswoman said after the company was informed that Mr. Trabelsi was a suspect in the sexual assault, the company immediately stopped contracting with both him and the sedan company he worked for, Capitol Limo.

Mr. Trabelsi and his family could not be reached for comment Thursday.